Electric flyers: How much current does your radio/ESC draw with switch off? - RC Groups
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May 25, 2009, 09:17 PM
Registered User

Electric flyers: How much current does your radio/ESC draw with switch off?

I have an older Futaba single-stick 8ch radio in a sailplane with a 40A ESC w/BEC. The ESC has a switch to be mounted on the plane, which turns the system on and off... I thought.

But I just measured the current draw from the battery (11.1V 2100 mAh 20C LiPo) with the switch off... 35 mA!

Quite a surprise. I expected maybe an order of magnitude less than that, like 3 mA or less. I mean, it's just sitting there doing nothing, receiving nothing. I thought turning a switch off, was supposed to mean OFF. Were's all that current going? I measured it two different ways, got the same answer both times.

With switch on and transmitter on, the currrent draw of the receiver, servos, and ESC while idling jumped to 75 mA, which was a little more what I expected (though still high?)

Do these numbers jive wih what you fellows are seeing in your systems?
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May 25, 2009, 09:58 PM
60 years of RC flying
Daedalus66's Avatar
It's not an on-off switch at all. It's simply a disarming switch to prevent the motor from running accidentally. The battery MUST be unplugged to turn the system off. Leaving the ESC plugged in will drain the battery in a few hours or days, very likely destroying a LiPo.
May 25, 2009, 10:15 PM
Deletedfor proving Nauga wrong
Turn the ESC's switch off and leave the TX on.. move the sticks. Often the RX is still powered and the servos will respond.
May 26, 2009, 01:26 AM
Registered User
It would be nice to have a switch that simply cuts off the battery, the way older (non-electric power) systems did. Of course, those systems didn't draw 40-plus amps at full power, they way present ones (including the one in my sailplane) do. If you open a set of switch contacts while that kind of current is flowing through it, your switch had better be built to handle it. And the switch may weigh more than the plane.

But this makes me wonder. Will I switch off that battery-cutoff switch, when the motor is running at full power? If I switch off the existing switch on the ESC, doesn't that GUARANTEE me that the motor will not be running at full power afterward? Maybe a less-hefty switch can be used, as a battery cutoff, as long as the ESC switch is always turned off first?

Of course, that battery cutoff switch had better be able to handle that 40 amps flowing through it, which obviously it WILL get during max-performance climbs, racing, etc. But a good switch should have nearly-zero ohms resistance, so a moderate-sized one, correctly designed, may be able to handle such a current. As long as it will NEVER be asked to interrupt that current itself.

Do such switches exist? Anyone know?

It would be nice to simply flip off a switch (or two) after flying, without having to pop the hatch, remove the battery (not easy in my plane) and unplug a pretty stiff connector. Am I dreaming?
May 26, 2009, 11:58 AM
Deletedfor proving Nauga wrong
for the switch to cut off all power drain out of the battery, it has to be in a wire between the battery and ESC.

I have added such switches to some models that have awkward access to the battery.
May 26, 2009, 12:35 PM
Registered User
Originally Posted by fhhuber506771
for the switch to cut off all power drain out of the battery, it has to be in a wire between the battery and ESC.
Egg-zactly. I wonder if there is such a switch, that can conduct 40A through its contacts, as long as it is assured that it will NEVER be switched off while that much current is flowing?
May 26, 2009, 12:43 PM
Deletedfor proving Nauga wrong
What a lot of people do is take a female deans plug.. wire it into the + lead. Take a make and jumper between poles. Remove the plug and the battery is disconnected.

Thats rated for appx 60 amps.


I found a large automotive toggle switch rated to turn on-off a 60 amp load.

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